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Glossary
The vocabulary of peptide research in plain language. Terms link to the compound profiles they relate to.
A
- Agonist
- A molecule that binds a receptor and activates it, producing a biological response. Full agonists produce a maximal response; partial agonists produce a submaximal response even at full receptor occupancy.
See:Antagonist, Receptor, GLP-1R (glucagon-like peptide-1 receptor)
- Amino acid
- An organic molecule containing an amine group and a carboxyl group. Twenty standard amino acids serve as the building blocks of peptides and proteins, linked in sequence by peptide bonds.
- Amylin
- A peptide hormone co-secreted with insulin by pancreatic beta cells. Acting through amylin receptors, it slows gastric emptying, suppresses glucagon after meals, and contributes to satiety signaling.
See:Cagrilintide, GLP-1, Glucagon
- Analog
- A molecule structurally modified from a naturally occurring compound, often by substituting or adding amino acids or chemical groups, to alter properties such as stability, half-life, or receptor selectivity.
See:Tesamorelin, Peptide, Half-life, Agonist
- Angiogenesis
- The formation of new blood vessels from existing vasculature. It is essential in development and tissue repair and also occurs in pathological processes such as tumour growth.
B
- Bacteriostatic water
- Sterile water containing a preservative, commonly 0.9 percent benzyl alcohol, that inhibits bacterial growth. It is used as a diluent where a multi-use container is intended.
- BDNF
- Brain-derived neurotrophic factor, a protein supporting neuron survival, growth, and synaptic plasticity. It is widely studied in relation to learning, memory, and mood regulation.
- Beyond-use date
- The date or time after which a prepared or opened preparation should no longer be used, based on stability and sterility considerations. Distinct from the manufacturer's expiration date for an unopened product.
- Bioavailability
- The fraction of an administered substance that reaches systemic circulation unchanged. Intravenous administration is defined as 100 percent; other routes are typically lower due to incomplete absorption or metabolism.
C
- Certificate of analysis (COA)
- A document reporting analytical test results for a specific batch of material, typically including identity, purity, and test methods, allowing verification against specifications.
See:HPLC, Mass spectrometry, Purity, Endotoxin
- Collagen
- The most abundant structural protein in mammals, forming a triple-helix fibre that provides tensile strength to skin, tendon, bone, and connective tissue. Rich in glycine, proline, and hydroxyproline.
See:GHK-Cu, Glow (BPC-157 + TB-500 + GHK-Cu), Amino acid, Angiogenesis
- Cycle
- A defined period during which a compound is given in a research protocol, typically followed by a period without it. The term is common in informal literature and less standardized than trial terminology.
See:Washout period, Titration
E
- Endotoxin
- Lipopolysaccharide from the outer membrane of Gram-negative bacteria, capable of triggering strong inflammatory responses. Levels are commonly measured with the Limulus amebocyte lysate (LAL) test and reported in endotoxin units.
G
- GCGR (glucagon receptor)
- A G protein-coupled receptor activated by glucagon, expressed mainly in the liver and also in kidney and adipose tissue. It mediates hepatic glucose output and influences energy expenditure.
- Ghrelin
- A peptide hormone produced mainly in the stomach, often called the hunger hormone. It stimulates appetite and growth hormone release by activating the growth hormone secretagogue receptor.
See:Ipamorelin, GHS-R1a (ghrelin receptor), Growth hormone, Secretagogue
- GHRH
- Growth hormone-releasing hormone, a hypothalamic peptide that stimulates synthesis and pulsatile release of growth hormone from the anterior pituitary.
See:Sermorelin, Tesamorelin, GHRH-R (growth hormone-releasing hormone receptor), Growth hormone
- GHRH-R (growth hormone-releasing hormone receptor)
- A G protein-coupled receptor on anterior pituitary somatotroph cells that binds GHRH and stimulates growth hormone synthesis and release.
See:Sermorelin, Tesamorelin, CJC-1295, GHRH
- GHS-R1a (ghrelin receptor)
- The growth hormone secretagogue receptor type 1a, a G protein-coupled receptor activated by ghrelin. Found in the pituitary and hypothalamus, it mediates growth hormone release and appetite signaling.
See:Ipamorelin, CJC-1295 + Ipamorelin, Ghrelin, Secretagogue
- GIP
- Glucose-dependent insulinotropic polypeptide, an incretin hormone secreted by intestinal K cells after nutrient intake. It enhances glucose-dependent insulin secretion and participates in fat metabolism.
See:Tirzepatide, GLP-3R, GIPR (glucose-dependent insulinotropic polypeptide receptor), GLP-1
- GIPR (glucose-dependent insulinotropic polypeptide receptor)
- A G protein-coupled receptor activated by GIP, expressed in pancreatic beta cells, adipose tissue, and the brain. It mediates GIP's insulinotropic and metabolic effects.
See:Tirzepatide, GLP-3R, GIP
- GLP-1
- Glucagon-like peptide-1, an incretin hormone secreted by intestinal L cells after food intake. It stimulates glucose-dependent insulin release, suppresses glucagon, slows gastric emptying, and is associated with satiety signaling.
See:Semaglutide, Tirzepatide, GLP-1R (glucagon-like peptide-1 receptor), GIP
- GLP-1R (glucagon-like peptide-1 receptor)
- A G protein-coupled receptor activated by GLP-1, expressed in the pancreas, brain, gut, and other tissues. It mediates glucose-dependent insulin secretion and satiety-related signaling.
See:Semaglutide, Tirzepatide, GLP-3R, GLP-1
- Glucagon
- A peptide hormone produced by pancreatic alpha cells that raises blood glucose by promoting hepatic glycogen breakdown and glucose production. It also influences energy expenditure and lipid metabolism.
- Growth hormone
- A protein hormone secreted by the anterior pituitary in pulses. It influences growth, body composition, and metabolism, many of its effects mediated by IGF-1 produced in the liver.
See:CJC-1295 + Ipamorelin, GHRH, Ghrelin, IGF-1
H
- Half-life
- The time required for the concentration of a substance in plasma or a sample to fall by half. Elimination half-life is a core pharmacokinetic parameter.
- HPLC
- High-performance liquid chromatography, an analytical technique that separates mixture components by passing them through a packed column under pressure. Commonly used to quantify peptide purity.
See:Purity, Mass spectrometry, Certificate of analysis (COA)
I
- IGF-1
- Insulin-like growth factor 1, a peptide hormone produced mainly by the liver in response to growth hormone. It mediates many growth-promoting effects and is commonly measured as a marker of growth hormone activity.
See:IGF-1, Growth hormone, GHRH
- In vitro
- Latin for "in glass." Refers to experiments performed outside a living organism, such as in cell cultures or test tubes. Results may not predict effects in whole organisms.
See:In vivo, Preclinical
- In vivo
- Latin for "within the living." Refers to experiments conducted in whole living organisms, such as animal models or humans.
See:In vitro, Preclinical
- International Unit (IU)
- A unit measuring a substance's biological activity rather than its mass, defined against an international reference standard. The mass equivalent of one IU differs from substance to substance.
See:HCG, Microgram (mcg), Syringe units
- Intramuscular
- Within skeletal muscle tissue. Intramuscular administration is a parenteral route described in research literature, generally with faster absorption than subcutaneous delivery owing to greater muscle blood flow.
- Intranasal
- Via the nasal cavity. Intranasal delivery has been studied as a route for some peptides because the nasal mucosa is highly vascularized and may offer a pathway toward the central nervous system.
See:Semax, Selank, Subcutaneous, Bioavailability
L
- Lyophilized
- Freeze-dried. Lyophilization removes water from a frozen material under vacuum by sublimation, producing a dry powder or cake that is generally more stable in storage than a solution.
M
- Mass spectrometry
- An analytical technique that measures the mass-to-charge ratio of ionized molecules. Used to confirm a peptide's identity by comparing observed molecular mass with the expected value.
- Melanocortin receptor
- A family of five G protein-coupled receptors (MC1R to MC5R) activated by melanocortin peptides derived from pro-opiomelanocortin. They participate in pigmentation, energy balance, inflammation, and sexual function.
- Meta-analysis
- A statistical method that pools results from multiple independent studies addressing a similar question to produce a combined estimate of effect, with greater statistical power than individual studies.
- Microgram (mcg)
- A unit of mass equal to one millionth of a gram, or one thousandth of a milligram. Also abbreviated µg.
- Mitochondria
- Membrane-bound organelles that generate most cellular ATP through oxidative phosphorylation. They also regulate calcium signaling and apoptosis and are a major source of reactive oxygen species.
See:SS-31, MOTS-c, NAD+, Oxidative stress
N
- NAD+
- Nicotinamide adenine dinucleotide in its oxidized form, a coenzyme central to cellular energy metabolism and redox reactions. It is also a required substrate for sirtuins and other enzymes.
See:NAD+, 5-Amino-1MQ, Sirtuins, Mitochondria
- NF-κB
- Nuclear factor kappa B, a family of transcription factors that regulate genes involved in inflammation, immune responses, and cell survival. Often measured as an inflammatory signaling marker in research.
See:KPV, KLOW (TB-500 + BPC-157 + GHK-Cu + KPV), Oxidative stress
O
- Oral bioavailability
- The fraction of an orally administered substance reaching systemic circulation. For most peptides it is low because of enzymatic degradation in the gastrointestinal tract and poor absorption across the intestinal lining.
- Oxidative stress
- An imbalance between production of reactive oxygen species and the capacity of antioxidant systems to neutralize them, which can damage lipids, proteins, and DNA.
See:Glutathione, SS-31, Mitochondria, NF-κB
P
- Peptide
- A short chain of amino acids joined by peptide bonds, typically fewer than about 50 residues. Longer chains are usually called proteins. Many hormones and signaling molecules are peptides.
See:Amino acid, Analog, Receptor
- Pharmacodynamics
- The study of how a substance affects an organism, including receptor binding, mechanism of action, and the relationship between concentration and biological effect.
See:Pharmacokinetics, Receptor, Agonist
- Pharmacokinetics
- The study of how an organism affects a substance over time, covering absorption, distribution, metabolism, and excretion. Often summarized by parameters such as half-life, peak concentration, and clearance.
- Phase 1 trial
- The first stage of human clinical testing, usually in small groups, primarily assessing safety, tolerability, and pharmacokinetics rather than efficacy.
- Phase 2 trial
- A clinical study in a larger group, often of people with the target condition, exploring preliminary efficacy, dose-response relationships, and further safety data.
- Phase 3 trial
- A large clinical study, often multicentre and randomized, designed to confirm efficacy and monitor adverse events in a broad population. Results typically support regulatory submissions.
- Placebo
- An inactive substance or sham procedure given to a control group so that effects of the active intervention can be distinguished from expectation effects and natural variation.
- Preclinical
- Research conducted before human testing, including in vitro and animal studies, to characterize mechanism, pharmacology, and toxicity. Preclinical findings frequently do not translate to humans.
See:In vitro, In vivo, Phase 1 trial
- Purity
- The proportion of a sample consisting of the intended compound, typically expressed as a percentage determined by HPLC peak area. It does not by itself confirm identity or absence of endotoxin.
See:HPLC, Mass spectrometry, Endotoxin, Certificate of analysis (COA)
R
- Randomized controlled trial
- A study in which participants are randomly assigned to an intervention or control group, such as placebo, to reduce bias. Often blinded. Considered a high-quality design for evaluating interventions.
- Receptor
- A protein, usually on the cell surface or inside the cell, that binds a specific signaling molecule and initiates a cellular response. Many peptide hormones act through G protein-coupled receptors.
- Reconstitution
- The process of returning a lyophilized material to liquid form by adding a suitable diluent, producing a solution of defined concentration for laboratory use.
S
- Secretagogue
- A substance that stimulates secretion of another substance. A growth hormone secretagogue, for example, prompts the pituitary gland to release growth hormone.
See:Ipamorelin, Sermorelin, Growth hormone, GHS-R1a (ghrelin receptor)
- Sirtuins
- A family of NAD+-dependent enzymes, SIRT1 to SIRT7 in mammals, that remove acetyl and other groups from proteins. They regulate metabolism, stress responses, and gene expression and are studied in aging biology.
See:NAD+, Mitochondria
- Subcutaneous
- Beneath the skin, in the fatty tissue layer above muscle. In research literature, subcutaneous administration is a common parenteral route for peptides, generally with slower absorption than intravenous delivery.
- Syringe units
- The graduation markings on an insulin-type syringe. They measure volume, not mass or biological activity; on a U-100 syringe one unit equals 0.01 mL.
T
- Telomerase
- A ribonucleoprotein enzyme that adds repetitive DNA sequences to chromosome ends (telomeres), offsetting shortening during cell division. Active in stem and germ cells, largely inactive in most adult somatic cells.
See:Epithalon
- Titration
- In clinical research, the stepwise adjustment of an amount over time according to a protocol, often to assess tolerability. In analytical chemistry, a method of determining concentration by controlled reagent addition.
See:Phase 2 trial, Cycle
U
- U-100 syringe
- A syringe calibrated for U-100 concentration, meaning 100 units per millilitre. Each graduation marked as one unit corresponds to 0.01 mL of volume.
V
- VEGF
- Vascular endothelial growth factor, a family of signaling proteins that stimulate endothelial cell proliferation and new blood vessel formation. A principal regulator of angiogenesis.
See:BPC-157, Angiogenesis
W
- Washout period
- An interval in a study during which no intervention is given, allowing a prior substance's effects to dissipate before another phase begins. Commonly used in crossover trial designs.
Definitions are editorial summaries for research context and may be pending review. See our methodology.
